When medical examiners step inside the yellow crime-scene tape, they bring expertise held by just a handful of people in the state. But do they do so as impartial sleuths who simply "follow the evidence," to borrow a phrase, or as public employees with their own loyalties and biases?

Or are they both?

The question is at the heart of an unusual dispute stemming from a Dakota County deputy medical examiner's work with a defense attorney in a Washington County murder trial last year. Dakota County Attorney James Backstrom took exception to a representative of a public office potentially calling prosecution evidence into question during a criminal trial, and his sharp e-mail exchange with medical examiner Dr. Lindsey Thomas led to accusations of coercion when the deputy medical examiner withdrew from the trial.

Thomas and some other Minnesota forensic pathologists say they have an obligation to lend their expertise to either side in a criminal trial, because their loyalty is to the truth, not to one side or the other.

But Backstrom argued that the practice of county-employed coroners testifying for the defense could jeopardize future cases and that it hurts the credibility of medical examiners, and by extension, county attorneys.

"If you wish to be a defense expert, you should not be a public official representing Dakota County as our coroner," Backstrom wrote in one of his e-mails to Thomas.

"One moment you're working for the Dakota County government structure. The next minute you're working for a private entity as an expert witness of a defense case in another particular county," Franklin said. "Where do you turn your county medical examiner experience on or off? Where's the light switch to do that?"

But Dr. John Howard, president of the National Association of Medical Examiners, said it's not that simple.

"It's not a simple answer or arrangement, but what we feel strongly about is we need to be independent," he said. "We need to be free of undue influence from anyone who has a special interest in any case. We should be allowed to render professional opinions."

Thomas said it's necessary for the state's few forensic pathologists to share their knowledge. Doing so, she says, helps their credibility because it shows they're interested in the truth, not acting out of allegiance to one side of the courtroom.

The design and practices of medical examiners' offices in Minnesota vary. But the number of forensic pathologists -- doctors who are qualified to be medical examiners -- is small. There are fewer than 500 nationwide and about 20 in Minnesota.

Some medical examiners, such as Thomas, are private employees of hospitals or forensics labs who work part time for counties on contract. Dakota and seven other counties will pay a combined $1.14 million in 2009 to use the morgue, facilities and staff, including Thomas, at Regina Medical Center in Hastings.

In 2008, the lab did about 350 autopsies for the counties under that contract, in addition to other work, including defense consultations, she said.

Other labs, such as the Hennepin and Anoka County medical examiner's offices, are full-time operations, paid for by the county.

In those counties, the medical examiners are allowed to offer their expertise to defense attorneys as long as it's on their own time.

"If we're not available to [defense attorneys], where would they go?" said Dr. Andrew Baker, the Hennepin County medical examiner.

But Dr. Tom Uncini, medical examiner for St. Louis and Koochiching counties in northern Minnesota, said forensic pathologists from his office are prohibited by contract from consulting or providing expert defense testimony.

"It makes it difficult to work with your neighbors," Uncini said, though noting that he's not philosophically opposed to the practice.

Concerns about money, ethics

The defense often pays its expert witnesses, and forensic pathologists and medical examiners charge hundreds of dollars per hour.

Ted Sampsell-Jones, a professor of criminal law and evidence at William Mitchell College of Law in St. Paul, said many experts do consulting to make additional money, but the payment is meant to give the defense access to the type of experts that prosecutors have on staff, not to buy specific testimony.

Thomas's office charges $300 an hour, but she said the money from defense consulting goes to Regina Medical Center to support the morgue, not to pad the paychecks of the medical examiner or her staff.

Howard said it shouldn't matter who is paying the medical examiner because testimony should be truthful and neutral.

"Lawyers always see it as you're testifying for or against," Howard said. "That's not really what good forensic pathologists do."